The present invention relates to a new process for preparing azidobenzal compounds.
Aromatic azido compounds are of industrial importance as crosslinking agents for coatings crosslinkable by light and which consist of certain polymeric compounds, for example photoresists based on cyclized polyisoprenes.
The 2,6-bis-[(4-azidophenyl)-methylene]-cyclohexanones of formula I ##STR4## wherein R is hydrogen or alkyl of 1-6 C atoms, are particularly frequently used as such crosslinking agents. Various processes are already known for their preparation, but they all have considerable disadvantages.
For example, according to U.S. Pat. No. 2,940,853, 4-azidobenzaldehyde is subjected to a condensation reaction with a cyclohexanone of formula (II) ##STR5## wherein R is as defined above. However, since 4-azidobenzaldehyde is an exceptionally explosive substance, its use requires extensive and expensive safety measures. According to German Offenlegungsschrift No. 2,064,597, the use of 4-azidobenzaldehyde can be avoided by subjecting 4-nitrobenzaldehyde to a condensation reaction with a cyclohexanone of formula (II). The nitro groups in the resulting 2,6-bis-[(4-nitrophenyl)-methylene]-cyclohexanones, which are likewise explosive, are then selectively reduced to amino groups. The latter are then converted into azido groups using conventional methods, by diazotization and reaction with sodium azide. In this process, hydrazine hydrate in the presence of Raney nickel is used for the selective reduction of the nitro groups. This process is also unsuitable for the preparation of 2,6-bis-[(4-azidophenyl)methylene]-cyclohexanones of formula (I) on an industrial scale because of the large amounts of Raney nickel required for the reduction.